1. Field of the Invention
The present invention relates to a cooling structure for an internal combustion engine in which: a spacer is fitted inside a water jacket formed to surround a periphery of a cylinder bore of a cylinder block in the internal combustion engine; and a cooling condition of the cylinder bore is controlled by regulating a flow of cooling water in the water jacket by use of the spacer.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2008-64054 has made publicly known such a cooling structure for an internal combustion engine in which: the inner peripheral surface of the spacer is put in contact with the inner wall surface of the water jacket of the cylinder block in one side where cooling water is introduced into the water jacket, while the inner peripheral surface of the spacer is kept away from the inner wall surface of the water jacket in the opposite side; and thereby, the temperature of the cylinder bores is made uniform throughout their entire peripheries.
Meanwhile, the sliding of the pistons inside the cylinder bores has a problem that: side thrusts acting on the pistons cause hitting sounds; and noises are caused by the propagation of the hitting sounds to the outer surface of the cylinder block via the water jacket. In particular, in a case where the spacer is fitted inside the water jacket, the noises are likely to increase because the hitting sounds of the pistons are transmitted via the spacer thereby to easily pass through the water jacket. However, the above-mentioned conventional cooling structure for an internal combustion engine has no specific measures against the problem that the attachment of the spacer increases the noises made by the hitting sounds of the pistons.